The invention relates to improvements in rolls of the type often used in calenders and analogous machines for the treatment of running webs of paper or other flexible sheet material.
It is well known to mount the cylindrical shell of a roll for use in a calender on a stationary carrier and to mount the ends of the shell on suitable antifriction bearings. The space between the bearings often accommodates a hydrostatic displacing unit serving to counteract undesirable flexing of the shell in response to the pressure which is applied thereto by a neighboring roll or by the treated material. The bearings at the ends of the shell are designed to take up axial and/or radial stresses. Reference may be had to German Offenlegungsschrift No. 24 20 324 which discloses a roll wherein the hydrostatic displacing unit comprises a row of supporting elements and hydraulic motors acting upon selected supporting elements to prevent excessive or any flexing of the rotating shell. The supporting elements are biased radially outwardly toward the internal surface of the rotating shell. As a rule, the external surfaces of the supporting elements are provided with pockets which receive pressurized hydraulic fluid by way of flow-restricting channels, and the fluid which leaks from the pockets enters the internal space of the shell.
It is also known to heat the shell of the roll to an elevated temperature which is necessary to properly treat the running web of paper or the like. Hydraulic fluid which is supplied to the motors for the supporting elements can serve to heat the shell to a selected temperature. The transfer of heat from the pressurized fluid to the shell is quite satisfactory because the bodies of fluid in the pockets of the supporting elements are in large-area contact with the internal surface of the shell. It is further known to admit hydraulic fluid into the shell and to bring such fluid into contact with the internal surface of the shell at locations other than those which are occupied by the supporting elements of the hydrostatic displacing unit. For example, if a single row of supporting elements is disposed between the upper side of the carrier and the uppermost portion of the internal surface of the shell, the roll can further comprise means for admitting heated hydraulic fluid against the lower portion of the internal surface of the shell opposite the row of supporting elements.
Hydraulic fluid which is used to operate the motors of the hydrostatic displacing unit is frequently used to lubricate the bearings at the axial ends of the hydrostatic unit. Such mode of lubricating simplifies the design of the roll because there is no need to provide a discrete lubricating system. However, this also brings about certain drawbacks because the temperature of the lubricant cannot exceed a preselected maximum value which is often well below the temperature to which the shell is to be heated.